Talk to field agent Keith Nance in Talos Island - he should appear automagically in your contact list once you hit Lv20. Mind you, at Lv30 and above, said arc is no longer available normally, though you can run it via a flashback.
Twisted Reflections from Keith Nance
Available from levels 20 to 30. If you outlevel it, it's located in the Flashback list near the middle of the 25-29 list.
EDIT: Damn you, Quinch! I was foiled by hunting down the link. 
@Roderick
Ty 
Hey guys. Today i was talking to a friend of mine and she said she was doing a story arc where you face a evil twin or something in Talos Island. Does anyone know which story arc it is? and if you actual face your evil twin or something?